Owen Smith’s leadership challenge has been lifted by a surge in grassroots' support with more than 500 Labour councillors backing him for the top job.

In a letter, the councillors said only Mr Smith had “the tenacity and skill” to help working people and unite the party.

They warned that the “stakes could not be higher” for the Labour Party as it decides between Mr Smith and Jeremy Corbyn .

“There are militants in both wings of our Party who are determined to carry out a civil war against each other, whether it harms working people or not.

“We have intimidation and bullying in Constituency Labour Parties up and down the country.

Labour councillors say only Owen Smith has the 'tenacity' to helping working people

“We have those who seem to prefer perpetual division to the job of winning power for the good of those we represent. We need a unifying leader who is principled and competent,” the letter said.

The organisers of the letter, Gedling councillor Michael Payne and Westminster councillor, Tim Roca, said their fellow councillors believed it would be “nearly impossible” to win a general election under Mr Corbyn.

“Councillors speak to real voters every day, and understand that winning a General Election with Jeremy Corbyn as leader will be nearly impossible.

“It is clear that councillors who see the effects of Tory austerity close up, and understand the consequences of permanent Tory government, overwhelmingly support Owen Smith to lead and unite the Labour Party ,” they said.

It came as a separate poll found the majority of Labour councillors in marginal Westminster seats are backing him over Jeremy Corbyn .

The survey of 350 Labour councillors in 250 marginal seats have 60% backing Mr Smith with 28% for Mr Corbyn. Just over 11% did not express an opinion.

And it found that 64.6% of the councillors believe Mr Smith is the candidate best placed to win the next general election, with just 23.4% naming the current Labour leader and 12% don’t knows.

But the poll by Labour History Research Unit at Anglia Ruskin University also showed the scale of the task facing the Welsh MP if he wants to oust Mr Corbyn.

It found the councillors thought that 37.7% of their members would still vote for Mr Corbyn, 34% did not know and only 28.3% believing they would back the challenger.

And the councillors believe that 53.4% of the 183,000 registered supporters who signed up last week will vote for the Labour leader with just 10.3% backing Mr Smith. The councillors said they did not know how the other 36.3% would vote.